[sdiy] Oberheim Xpander Res fail

[Tom Wiltshire]

Hi Csaba,

> Interesting thing . After measuring CV outputs coming from the U816  on the voice board the RES line of them was slightly higher than the others
> Measured on C820 VOICE1    2.153V
> 			C821  VOICE2    2.145V
> 			C823  VOICE3   2.127V
>                       C824  VOICE4   2.119V
> 			C825 VOICE 5   2.130V
> 			C826  VOICE6   2.127V

I'd be surprised if any of those values are unusual. That looks like reasonable variation to me. If one said 2.9V or 1.5V I'd worry, but not like that.

> (shouldn't this be values in the 5V range as it is fully open ?)

5V might be the maximum that it *could* go up to, but if it's scaled so that it only goes as far as the oscillation break point, that could be a lot lower. That looks to be the case here. Incidentally, the datasheet for CEM3372 says 2.8V is the typical Res CV for oscillation, but gives a range from 2.2 to 3.4V. That might suggest your values are a bit low, but if it oscillates fine, then it's ok. The other changes to the filter circuit might explain the difference, although I don't see immediately why. After all, the Xpander's filter isn't exactly a datasheet application of the chip!

> Now this was measured with Resonance fully open the value is 63. Then lowered the value to 0 and ended up with a negative  measurement of -52.7.

-52.7 what? mV?

Thanks,
Tom